feat: 添加好友功能并集成 LiteLLM 代理服务

- 新增好友搜索、添加、好友列表功能
- 集成 LiteLLM 代理服务及多模型定价配置
- 更新 iOS CocoaPods 配置
- 更新 .gitignore 和环境变量配置

backend/src/core/config/settings.py

@@ -170,6 +170,17 @@ class LlmSettings(BaseModel):
     provider_keys: dict[str, str] = Field(default_factory=dict)
 
 
+class LiteLLMSettings(BaseModel):
+    host: str = "127.0.0.1"
+    port: int = 3875
+    api_key: str = "sk-local"
+
+    @computed_field
+    @property
+    def base_url(self) -> str:
+        return f"http://{self.host}:{self.port}/v1"
+
+
 class DatabaseSettings(BaseModel):
     host: str = "localhost"
     port: int = 5432
@@ -206,6 +217,7 @@ class Settings(BaseSettings):
     supabase: SupabaseSettings = Field()
     storage: StorageSettings = StorageSettings()
     llm: LlmSettings = LlmSettings()
+    litellm: LiteLLMSettings = LiteLLMSettings()
     agent_runtime: AgentRuntimeSettings = AgentRuntimeSettings()
     taskiq: TaskiqSettings = TaskiqSettings()
     database: DatabaseSettings = DatabaseSettings()